Friction test apparatus and method
A friction test apparatus includes a base structure and a receptacle secured to the base structure. At least three lower friction surfaces are positioned in the receptacle. The friction test apparatus includes a motor having a rotatable shaft providing powered rotation of the shaft. An upper friction surface is positioned on the shaft in contact with the at least three friction surfaces in the receptacle. The receptacle includes a fluid inlet and a fluid outlet to permit a fluid in the receptacle to be changed.
The present application is a divisional of U.S. patent application Ser. No. 10/439,405, filed May 16, 2003, which claims the benefit of U.S. Provisional Application No. 60/381,479, entitled FOUR-BALL WEAR TEST MACHINE, filed on May 17, 2002, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION Various four-ball test machines have been developed to evaluate the friction and wear characteristics of lubricants such as motor oils, hydraulic oils, cutting fluids, greases, solid lubricants or the like. Existing four-ball testers can also be used to evaluate the friction wear characteristics of bearing materials. In this case, the test balls themselves would be made of the material to be tested, and the same lubricant fluid would be utilized for the various varying materials to be tested. Known four-ball testers include a test cup with three steel balls positioned inside the test cup. The steel balls are held very tightly together by a conical ring that is secured via threaded fasteners to lock the balls in place. A typical four-ball test machine utilizes three steel balls that are ½ inch in diameter. A test fluid is placed inside the cup covering the three balls. With reference to
The amount of force pushing the three balls in the test cup 2 against the ball on the rotating spindle 9 can be varied by changing the weights 7. Typical lever arms 6 have a 10-to-1 ratio such that a four-kilogram weight 7 causes the bottom three balls in the test cup 2 to push up against the rotating top ball on spindle 9 with a force of 40 kg.
During a typical four-ball wear test 3 new test balls are placed into a clean test cup 2 and clamped securely in place above the heater block 3. The test fluid is then added to the test cup 2, and a new test ball is secured to the shaft 9. Shaft 9 includes a chuck (not shown) that secures the upper test ball to the shaft 9. During the test, the heater block 3 is turned on, and the temperature of the test fluid in the test cup 2 is monitored. When the test fluid reaches the test temperature, the load is applied and the motor 11 is actuated to thereby rotate the spindle 9.
A common ASTM test method utilizes a load of 40 kg, and is run at 1200 rpm at 75° C. for one hour. At the end of the test run the motor is stopped, the heater is turned off, the load is removed, and the test cup 2 is taken off the tester 1.
The thrust bearing 4 under the heater 3 allows the heater 3 and test cup 2 to rotate freely and also to move horizontally because one of the races of the thrust bearing 4 is replaced with a flat hard steel surface. With this arrangement, the cup 2 can freely move in any direction and center itself under the top rotating ball that is secured to the shaft 9. The top ball contacts each of the three bottom balls in the test cup 2. Upon rotation of the top ball, a force is transmitted to the test balls in the test cup 2, tending to rotate the test cup 2. However, a load cell 12 is contacted to the heater block 3 via a small chain 13 that prevents rotation of the heater block 3 and test cup 2. The load cell 12 is utilized to measure the rotational force acting on the test cup 2, and to thereby calculate the coefficient of friction.
Upon completion of the test, the test cup is removed from the tester 1, and the test lubricant is drained. The cup 2 with the three bottom test balls still locked in place is placed under a microscope to measure the wear scars. The wear scars result from the top ball rotating against each of the bottom three balls under the test load. The wear scars are measured for each of the bottom three balls. In general, each of the three bottom balls will have a wear scar that is very similar in size and shape to the other two lower test balls. A measurement is made with a microscope of each wear scar diameter, in both the vertical and horizontal direction. A total of six measurements are taken, two for each ball, and then the average of the six readings is considered to be the wear scar diameter for a given test fluid under a specific test method.
The torsional forces that have been measured with the load cell 12 can also be averaged out over the test period and can be used to calculate the average coefficient of friction for a given test fluid under specific test conditions. Two characteristics of a lubricant can be determined in this way: 1) the coefficient of friction of the fluid; and 2) the amount of wear that occurred in the presence of the test fluid under given test conditions.
Upon completion of a test utilizing a first test fluid, another lubricant or a modified formula of the same lubricant, can be run under the same test conditions, and the friction wear characteristics can be compared with those of the first lubricant.
As discussed above, the four-ball test provides information concerning: 1) the average wear-scar diameter; and 2) the average coefficient of friction, or a full friction trace for the test duration. The type of signal processing system attached to the tester will determine whether the average coefficient of friction or a full friction trace is produced by the test.
One frequent use for four-ball testers is as a quality control check for hydraulic fluids. Such tests commonly utilize a 40 kg load at 1200 rpm and 75° F. with a one hour duration. Other applications for four-ball tests include quality control tests for automatic transmission fluids. Four-ball tests are also used for quality control for many other automotive or other fluids such as brake fluids, motor oils, gear oils, torque fluids, mineral based cutting oils, water based cutting oils, and other fluids. A variety of fluids or semi-fluids for which wear and friction value are of importance can be tested using four-ball friction wear testing. The wear scar diameter and friction value can also be utilized to determine if a material has a proper composition. In such testing, the test balls are made of the material to be tested, and a lubricant having known properties is utilized.
Four-ball test equipment can also be utilized to formulate the various fluids discussed above. For example, if a fluid includes a component that is no longer available, a fluid including a replacement component can be tested to determine if the new formulation has beneficial or detrimental friction and wear characteristics. Still another use for four-ball testers is to monitor the condition of fluids during use to determine when they are no longer acceptable, or when an additive to the fluid is needed.
As discussed above in connection with
However, existing four-ball testers such as those illustrated in
Pneumatic four-ball testers (
Furthermore, the air bearing utilized with such four-ball testers may also suffer from various drawbacks. For example, because the air bearing is on top of the air cylinder that applies the load, the pressure of the air bearing needs to be higher than the pressure applied by the air cylinder. This may result in a higher load than expected. Also, air bearings may allow the test cup to tilt slightly, resulting in uneven wear scars and unreliable test results.
Accordingly, a four-ball tester alleviating the problems of existing arrangements would be desirable.
SUMMARY OF THE INVENTIONOne aspect of the present invention is a friction test apparatus including a base structure and a receptacle secured to the base structure. At least three lower friction surfaces are positioned in the receptacle. The friction test apparatus includes a motor having a rotatable shaft providing powered rotation of the shaft. An upper friction surface is positioned on the shaft in contact with the at least three friction surfaces in the receptacle. The receptacle includes a fluid inlet and a fluid outlet to permit a fluid in the receptacle to be changed.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in
With reference to
The base assembly 21 includes a base plate 27 having feet 28 to support the four-ball test apparatus 20 on a worksurface 28. Front and rear vertical support members 29 and 30, respectively, are secured to the base plate 27, and extend vertically upwardly. The horizontal support member 24 is secured to the vertical members 29 and 30. An upper cross-member 31 is secured to intermediate vertical member 32. As described in more detail below, a pair of lift members 33 can be shifted vertically by routing handle 34 of lift assembly 25 to thereby lift the motor/weight assembly 22 out of engagement with the test cup 23 between tests for set up purposes, and the like.
The motor/weight assembly 22 includes an upper plate 40 and lower plates 41 and 42. A pair of vertical support members 43 are rigidly secured to the upper plate 40 and the lower plates 41 and 42. The vertical support members 43 are spaced apart, such that the support member 24 extends between the vertical supports 43 (see also
The motor/weight assembly 22 further includes a lower vertical member 49 that is secured to the lower plates 41 and 42 and extends downwardly therefrom towards the base plate 27. A support member such as plate 50 is secured to the lower end of vertical member 49 to thereby support weights 51. Weights 51 are flat plate members having a slot 52 to provide clearance for the vertical member 49 such that the center of gravity of the weights 51 can be positioned at or near the center line of vertical member 49. An extension 53 at the lower end of vertical member 49 engages an anti-swing assembly 54 to prevent swinging of motor/weight assembly 22. With further reference to
With reference to
With further reference to
With further reference to
Because the test cup of the present four-ball test apparatus 20 is rigidly secured to the support member 24, additional instruments or other connections can be made to the test cup itself without introduction of errors that would occur in existing test cup designs wherein the test cup “floats” on a thrust bearing or the like.
With reference to
With further reference to
The formulation attachment 95 and test cup 85 illustrated in
With further reference to
In addition to the advantages discussed above, the four-ball test apparatus 20 of the present invention also permits measurement of conductivity. The wear scar diameter and the deposits that form around the wear scar in the test balls provides useful information concerning a lubricant. However, the electrical resistance or impedance or capacitance provides valuable information concerning whether or not the test balls are making metal to metal contact, or if there might be some degree of separation by way of a very thin film of an insulating, organic nature. All of these can be measured with relative ease utilizing the four-ball test apparatus 20 of the present invention. The test cup is fixed so any required wiring can attached directly to the cup. The shaft of the motor can be readily fitted with a high quality slip ring to complete the circuit.
With further reference to
In contrast to such conventional chucks, the chuck 110 of the present invention illustrated in
The fifteen degree taper provides sufficient friction to ensure that the test ball 73 does not spin within the chuck 110, but permits simple removal of the test ball 73 from the chuck 110. During testing, the top test ball 73 is placed in the cup on top of the lower test balls 83, and the motor/weight assembly 22 is then brought downwardly by operation of lift assembly 25. The chuck 110 automatically engages the top ball 73 and centers the motor/weight assembly 22 on the lower test balls 83 in the test cup. The relatively low taper of the side walls provides sufficient friction during wear or friction testing to prevent sliding of test ball 73 in chuck 110, yet also prevents binding of the upper test ball 73, such that it drops out of the chuck 110 when the motor/weight assembly 22 is lifted utilizing the lift assembly 25. It is anticipated that sufficient force could be utilized with the four-ball test apparatus 20 of the present invention to permit such extreme pressure testing. One example of such a test is ASTM D-2783 “Measurement of Extreme Pressure Properties of Lubricating Fluids (Four Ball Method)”.
The four-ball test apparatus of the present invention ensures that all frictional forces measured by the load cell are due to the frictional engagement between the upper test ball 73 and the lower test balls 83, and eliminates potential errors caused by thrust bearings or the like in prior four-ball test arrangements. Furthermore, because the test cup is rigidly clamped, and does not move, various instruments or fluid lines or the like may be connected to the test cup without introducing additional sources of error in the test measurements.
In the foregoing description, it will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed herein. Such modifications are to be considered as included in the following claims, unless these claims by their language expressly state otherwise.
Claims
1. A method of testing the frictional characteristics of a lubricant, comprising:
- providing a friction test apparatus having a test receptacle with at least three lower friction surfaces and at least one upper friction surface in contact with the at least three lower friction surfaces, the test receptacle having a fluid outlet;
- providing lubricant in the test receptacle;
- rotating the upper friction surface about a generally vertical axis at a generally constant rate for a selected period of time with the upper friction surface engaging the lower friction surfaces; and
- removing lubricant from the test receptacle via the fluid outlet.
2. The method of claim 1, wherein:
- lubricant exiting the test receptacle through the fluid outlet is recirculated through a fluid conduit and pumped into the fluid inlet.
3. The method of claim 2, including:
- adding lubricant to the test receptacle to recirculate the lubricant; and
- introducing the additive to the lubricant after the lubricant is recirculated through the test receptacle.
4. The method of claim 3, wherein:
- the additive is added after at least one frictional characteristic of the test apparatus has stabilized.
5. The method of claim 4, wherein:
- the friction of the upper friction surface and the lower friction surfaces is measured and the additive is added after the friction has stabilized.
6. The method of claim 1, including:
- measuring the conductivity between the test receptacle, three lower friction surfaces, and upper friction surface.
7. The method of claim 1, wherein:
- the lubricant comprises a first lubricant added to the test receptacle and has a first composition;
- the first lubricant is circulated through the test receptacle for a selected period of time by adding and removing the first lubricant and including:
- displacing the first lubricant with a second lubricant having a second composition that is different than the first composition using the same upper friction surface and lower three friction surfaces.
8. The method of claim 7, including:
- circulating a reference lubricant through the test receptacle to determine if test conditions have changed, the reference lubricant having a composition that is different than that of the first and second lubricants.
9. The method of claim 1, wherein:
- the upper and lower friction surfaces are spherical.
10. A friction test apparatus, comprising:
- a base structure;
- a receptacle secured to the base structure;
- at least three lower friction surfaces positioned in the receptacle;
- a motor having a rotatable shaft, the motor providing powered rotation of said shaft;
- an upper friction surface positioned on the shaft and engaging the at least three lower friction surfaces in the receptacle, the receptacle including a fluid outlet to permit a fluid in the receptacle to be removed without disengaging the upper friction surface from the at least three lower friction surfaces.
11. The friction test apparatus of claim 10, including:
- a sensor operably connected to the motor to measure the torque generated upon rotation of the shaft.
12. The friction test apparatus of claim 10, wherein:
- the receptacle defines a sidewall, and includes a passageway through the sidewall forming an inlet.
13. The friction test apparatus of claim 12, wherein:
- the outlet comprises a passageway through the sidewall.
14. The friction test apparatus of claim 10, including:
- a fluid reservoir fluidly coupled to the receptacle to provide fluid flow from the reservoir into the receptacle.
15. The friction test apparatus of claim 14, including:
- a pump adapted to pump fluid from the reservoir into the receptacle.
16. The friction test apparatus of claim 15, including:
- a first conduit fluidly connecting the pump to the receptacle; and
- a second conduit fluidly connecting the fluid outlet to the reservoir.
17. The friction test apparatus of claim 13, wherein:
- the receptacle includes a first aperture through the sidewall forming an inlet; and
- the outlet comprises a second aperture through the sidewall located above the first aperture.
18. The friction test apparatus of claim 10, wherein:
- the lower friction surfaces comprise at least three lower test balls;
- the upper friction surface comprises at least one upper test ball; and
- the receptacle comprises a test cup including a clamp securely holding the three lower test balls in the test cup.
19. The friction test apparatus of claim 18, including:
- a ceramic chuck member on the shaft of the motor, the chuck member having an aperture partially receiving the upper test ball.
20. A friction test apparatus, comprising:
- a support structure;
- at least one upper friction member operably coupled to the support structure;
- at least one lower friction member operably coupled to the support structure and contacting the upper friction member for relative movement therebetween;
- a receptacle defining a cavity configured to hold a test fluid therein, the lower friction member at least partly disposed in the receptacle;
- a reservoir fluidly coupled to the receptacle to provide fluid flow from the reservoir into the receptacle; and
- a sensor determining the frictional force generated by movement of the upper and lower friction members relative to one another.
21. The friction test apparatus of claim 20, including:
- a motor providing powered movement of the upper friction member relative to the lower friction member.
22. The friction test apparatus of claim 21, including:
- a force-generating mechanism that provides an adjustable force that pushes the upper and lower friction members together.
23. The friction test apparatus of claim 20, wherein:
- the upper friction member comprises an upper test ball; and
- the lower friction member comprises at least three lower test balls.
24. The friction test apparatus of claim 23, wherein:
- the receptacle comprises a test cup defining a cavity that receives the three lower test balls.
25. The friction test apparatus of claim 24, wherein:
- the test cup includes an aperture that fluidly connects the cavity to the reservoir.
Type: Application
Filed: Nov 23, 2004
Publication Date: Apr 7, 2005
Patent Grant number: 7373800
Inventor: Joachim Domeier (Ann Arbor, MI)
Application Number: 10/996,255